Beam shaping device, system for launching a light beam into an optical fibber, and beam rotation unit for such a beam shaping device or such a system

ABSTRACT

The invention relates to a device for shaping the cross-section of a light beam, comprising at least one beam shaping unit with beam splitting means, beam deflecting means and beam combination means. The beam splitting means are capable of splitting a light beam which is incident on the beam shaping unit into two partial beams. The beam deflecting means are capable of deflecting at least one of the partial beams onto the beam combination means, and said beam combination means are capable of combining the two partial beams in such a manner that the cross-section of the light beam emerging from the beam shaping unit is reduced in size in one direction compared to the light beam incident on the beam shaping unit. The beam combination means is configured as a polarisation-selective beam splitting and beam combination unit that comprises at least two elements with an interface interposed in between. The two split partial beams can be incident on the interface from different directions.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a device for shaping the cross sectionof a light beam, including at least one beam shaping unit, with beamsplitter means, beam deflection means and beam combining means, the beamsplitter means being able to divide a light beam which is incident onthe beam shaping unit into two component beams, the beam deflectionmeans being able to deflect at least one of the component beams onto thebeam combining means, and the beam combining means being able to combinethe two component beams, such that the cross section of the light beamemerging from the beam shaping unit compared to the light beam enteringthe beam shaping unit is reduced in at least one direction.

[0002] Furthermore this invention relates to an arrangement for couplinga light beam which proceeds from an elongated laser light source with anelongated cross section into an optical fiber, comprising a laser lightsource, at least one collimation unit for collimating the light beamwhich emerges from the laser light source, and at least one focusingunit for focusing the light beams onto an optical fiber.

[0003] Furthermore the invention relates to a beam rotation unit for onesuch device, the beam rotation unit comprising at least one prism whichcan be located in the beam path of at least one light beam such that thecross section of the light beam passing through at least one prism canbe turned by at least two reflections, especially rotation by 90° beingable to take place.

[0004] A device of the aforementioned type and an arrangement of theaforementioned type are disclosed by German patent DE 195 37 265 C1. Inthe embodiment of a beam shaping unit which is described in it arhomboid prism pair which separates the incident radiation into twocomponent beam pencils is used as the beam splitter means. The beamdeflection means is two half cubic prisms which are integrated into thecorresponding component beam paths, as a result of the relatively longpath of the component beam pencil which has been traversed in this beamshaping unit there being another lens located between the rhomboid prismpair and the half cubic prisms. The beam combining means is a fifthprism which deflects the component beam pencils, which are incident onit, and combines them again.

[0005] The disadvantage in such a beam shaping unit is that a total ofseven components are used, each of the individual component beamspassing through either optionally partially absorbing surfaces ofoptical components and each being reflected on two other surfaces of theaforementioned components which may not be 100% reflective. As a resultof the many surfaces which must be transmitting or on which there mustbe reflection, a relatively high cost must be borne to improve thesesurfaces accordingly with regard to transmission and reflection. Inparticular, when several of these beam shaping units are set up insuccession, such a beam shaping device will be less effective.Furthermore, as a result of the many components, which are used, and thehigh improvement cost these beam shaping units will be extremelyexpensive.

[0006] An arrangement of the initially mentioned type is generally usedwhen for example the laser radiation emerging from a laser diode bar isto be focused on an optical fiber. In particular, as a result of thealmost line-shaped laser light source with individual emission centerswhich are located spaced apart over the length of the line and thedifferent divergences in the slow axis direction and fast axisdirection, it is a good idea to use a beam shaping device of theinitially mentioned type in order to repeatedly shape or fold togetherthe laser light emerging from the laser diode bar with an almostline-shaped cross section so that a laser beam pencil with an almostsquare cross section is formed which can then be more easily focused onan optical fiber. The effectiveness and economic efficiency of thisarrangement arises of course from the effectiveness and economicefficiency of the beam shaping unit used in it.

[0007] A beam rotation unit of the initially mentioned type is knownfrom U.S. Pat. No. 5,513,201. By means of the beam rotation unitsdescribed in it the laser radiation emerging from the laser diode barswill be focused on an optical fiber. In the already describeddivergences in the slow axis and the fast axis direction of the laserlight emerging from the laser diode bars rotation of the individuallight beams is a good idea because in this way the divergences in theslow axis direction and the fast axis direction can be interchanged. Thebeam rotation units described in the aforementioned US patent use prismsfor beam rotation. These prisms are however extremely complex instructure and can only be produced with a very high fabrication cost.

[0008] The object of this invention is to devise a beam shaping deviceof the initially mentioned type, a beam rotation unit and an arrangementof the initially mentioned type with an effective and economicalstructure.

SUMMARY OF THE INVENTION

[0009] The beam combining means is made as a polarization-selective beamsplitter and beam combination unit which includes at least two partswith a boundary surface which is located between them, and the twoseparated component beams can be incident on the boundary surface fromdifferent directions, and depending on their linear polarization one ofthe component beams can pass the boundary surface unhindered and theother of the component beams can be reflected on the boundary surface sothat the two component beams are combined in the area of the boundarysurface and leave the beam splitter and beam combination unitessentially at the same location in the same direction. Thispolarization-selective beam splitter and beam combination unit makeavailable a beam shaping unit in which one of the beams passes throughthe aforementioned boundary surface essentially without reflection,conversely the other of the beams is completely reflected on theboundary surface so that losses hardly occur. Especially the beamsplitter and beam combination unit can be located in the beam path ofthe light beam which is incident on it such that it is used both as abeam splitter means and also a beam combination means in which the firstcomponent beam is incident directly on the first entry surface of thebeam splitter and beam combination unit, conversely the second componentbeam can run past the first entry surface and can be deflected by thebeam deflection means onto the second entry surface. In this way thenumber of reflections and transmissions is further reduced.

[0010] A beam splitter and beam combination unit as claimed in theinvention can be made at least in sections of a double-refractingmaterial and can be made for example as a Glan-Thompson prism.

[0011] Alternatively the beam splitter and beam combination unit can bemade as a so-called polarization cube, the polarization cube consistingof two essentially identical prism-like parts which form a boundarysurface along one diagonal surface of the cube with one another. Atleast one of the two prism-like parts can be provided with apolarization-selective coating in the area of the boundary surface. As aresult of this coating these polarization cubes can be made such that ata certain angle the light beams of a first linear polarizationdirection, which are incident on the boundary surface, are completelyreflected, conversely light beams of a second direction which isperpendicular to the first linear polarization direction pass throughthe boundary surface. If the two component beams are incident on thepolarization cube from different directions which include an angle of90° with one another, and the boundary surface is oriented such that thebisector of the angle between the incidence directions of the twocomponent beams lies in the plane of the boundary surface, the componentbeams can be joined as a result of the above describedpolarization-selective reflection or transmission on the boundarysurface and leave the beam splitter and beam combination unitessentially at the same location in the same direction.

[0012] According to one preferred embodiment of this invention, the beamshaping unit is made from a polarization rotation element which canrotate the linear polarization of one of the two component beams,especially by an angle of 90°. In this way it is ensured that one of thetwo component beams is reflected on the boundary surface, conversely theother of the two component beams is transmitted. Here it is assumed thatthe incident light beam, which is to be split into two component beams,is essentially linearly polarized, as is generally the case in laserbeams. For the case in which the incident light beam is not linearlypolarized or is so only to a small degree, a linear polarizer should beconnected upstream in order to ensure the combination of the componentsbeams as claimed in the invention in the beam splitter and beamcombination unit.

[0013] The polarization rotation element can be made as a halfwavelength plate. This is a simple and proven embodiment of thepolarization rotation element.

[0014] Alternatively the polarization rotation element can be made as aprism, which is arranged such that the cross section of thecorresponding component beam is turned during passage through the prism,especially by 90°, in this way the corresponding rotation of the linearpolarization of this component beam taking place. A prism arranged inthis way represents a very elegant embodiment of a polarization rotationelement because the prism can perform still other functions. There isfor example the possibility that the prism is used at the same time asthe beam deflection means, then in the prism the corresponding componentbeam being able to be reflected, especially reflected twice. In this waythe number of transmissions and reflections is likewise reduced.

[0015] The beam deflection means can furthermore or alternatively bemade of a mirror, which can be located preferably at an angle of 45° inthe second of the two component beams. In particular it can be providedthat the prism, the mirror and the beam splitter and beam combinationunit are arranged such that a component beam can be directly incident onthe first entry surface of the beam splitter and beam combination unit,conversely the second component beam is reflected by the mirror into theprism, in which the beam cross section of the component beam is turnedby 90° and from which the component beam can enter the second entrysurface of the beam splitter and beam combination unit. In this way thenumber of reflections and transmissions for the two component beams isminimized, at the same time very elegant beam deflection andpolarization rotation being achieved by the prism.

[0016] According to one preferred embodiment of this invention, thedevice includes more than one beam shaping unit which are located insuccession such that the cross section of the light beam changes in eachof the beam shaping units, especially can be reduced in one direction.In this way especially a laser beam emerging from a laser diode bar canbe repeatedly reduced in one direction such that the arrangement asclaimed in the invention for coupling into the optical fiber can beoptimized.

[0017] According to another preferred embodiment of this invention, thedevice include more than one beam shaping unit which are located next toone another such that light beams emerging from the light sources whichare next to one another can be changed in the beam shaping units locatednext to one another, in particular can be made smaller in one direction.In this way for example in an arrangement as claimed in claim 17 thelight beams emerging from the individual emission centers of a laserdiode bar can be changed at the same time in the beam shaping unitswhich are located next to one another with respect to their beam crosssection.

[0018] In doing so the beam shaping units located next to one anothercan comprise an array of prisms, each of the individual prisms of thearray being used at the same time as a polarization rotation element andas a deflection means of each of the individual beam shaping units. Bycombining the individual prisms into an array, an embodiment of the beamshaping units which are located next to one another, which embodimentcan be economically produced, is devised. Moreover such an array can bemore easily managed because the distances of the individual prisms toone another and the orientation of the individual prisms to one anothercan be dictated by the production process. Optionally there is thepossibility of integrating the other elements of the beam shaping unitinto the array or mounting it securely on the array at the factory.

[0019] It is quite possible to arrange several arrays or several beamshaping units formed by these arrays in succession in order to changethe cross section of the individual light beams successively in theunits which are located behind one another.

[0020] In a beam rotation unit, it is provided that at least one prismhas two base surfaces which are made as isosceles right triangles andthree rectangular prism surfaces, and the light beam passing through atleast one prism can be reflected on the two prism surfaces which extendbetween the legs of the base surfaces. The structure of the prism assuch an isosceles right-angle prism constituted a very simple andeconomically producible choice.

[0021] In particular, it is possible for the beam rotation unit toinclude a number of prisms, which are combined into an array so that thecross sections of the light beams proceeding from the light sourceswhich are located next to one another can be rotated. Such an array ofprisms can then be integrated for example into an arrangement in orderto rotate the light beams emerging from the individual emission centersof the laser diode bar in order to cause exchange of the fast axisdivergence with the slow axis divergence. This array of cylinder lensescan be more easily produced in contrast to the beam rotation units,which are known.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other features and advantages of this invention become clear fromthe following description of preferred embodiments with reference to theattached figures:

[0023]FIG. 1 shows a schematic side view of one embodiment of a deviceas claimed in the invention;

[0024]FIG. 2a shows the beam cross section of a light beam beforeentering the device as shown in FIG. 1;

[0025]FIG. 2b shows the cross section of the light beam as shown in FIG.2a after passing through the device as shown in FIG. 1;

[0026]FIG. 3a shows a top view of another embodiment of a device asclaimed in the invention;

[0027]FIG. 3b shows a side view of the device as shown in FIG. 3a;

[0028]FIG. 4a shows the cross section of a light beam before enteringthe device as shown in FIG. 3;

[0029]FIG. 4b shows a cross section of the light beam as shown in FIG.4a after passing through the device as shown in FIG. 3;

[0030]FIG. 5 shows a schematic top view of another embodiment of adevice as claimed in the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0031] As is apparent from FIG. 1, the first embodiment of a device asincludes a beam shaping unit with a polarization selective beam splitterand beam combination unit 1, a mirror 2 and a polarization rotationelement 3. The beam splitter and beam combination unit 1 is made as apolarization cube. This polarization cube generally is made of silicaglass or a comparable material and has two prism-shaped halves 4, 5which are connected to one another along a diagonal boundary surface 6of the cube, especially cemented to one another. The boundary surface 6is provided with an especially multilayer polarization-selectivecoating. As a result of this coating, these polarization cubes can bemade such that light beams of a first polarization direction which areincident at a certain angle on the boundary surface 6 are totallyreflected, conversely light beams of a second direction which isperpendicular to the first direction pass through the boundary surface.The invention exploits this effect, as will be examined below.

[0032]FIG. 1 shows a light beam 7 a, b, c, d running from the left, i.e.in the Z direction, onto a beam shaping unit consisting of a beamsplitter and beam combination unit 1, mirror 2 and polarization rotationelement 3 comprised by the device as claimed in the invention. The lightbeam 7 a, b, c, d has a cross section 8 which is shown in FIG. 2a.Furthermore it is indicated in FIG. 1 and FIG. 2a that the light beam 7is linearly polarized in the X direction; this is illustrated by thearrows 9. The illustrated component means 7 a, 7 b, 7 c, 7 d of thelight beam 7 represent sample component beams.

[0033] The beam 7 is thus divided into two component beam pencils 7 a, 7b, and 7 c, 7 d by the first component beam pencil 7 a, 7 b beingincident perpendicularly on the first entry surface 10 of the beamsplitter and beam combination unit 1 and passing through it. Converselythe second component beam pencil 7 c, 7 d runs past the bottom of thebeam splitter and beam combination unit 1 and is incident on the mirror2 which is aligned in FIG. 1 at 45° to the entering component beampencil 7 c, 7 d. From this mirror the component beam pencil 7 c, 7 d isreflected in the X direction or in FIG. 1 to the top and is incident onthe second entry surface 11 of the beam splitter and beam combinationunit 1 which includes a right angle with the first entry surface 10.

[0034] The polarization rotation element 3 which is encompassed by thebeam shaping unit is arranged in the embodiment shown in FIG. 1 suchthat the second component beam pencil 7 c, 7 d before being incident onthe mirror 2 passes through the polarization rotation element 3.Alternatively the polarization rotation element 3 could also be locatedbetween the mirror 2 and the second entry surface 11 of the beamsplitter and beam combination unit 1. The polarization rotation element3 rotates the linear polarization of a passing light beam by 90°. Thepolarization rotation element 3 can be made for example as a halfwavelength plate.

[0035] As is apparent from FIG. 1, the beam splitter and beamcombination unit 1 made as a polarization cube is made and arranged suchthat the first component beam pencil 7 a, 7 b entering the first entrysurface 10 is incident on the boundary surface 6 at an angle of 45°,passes essentially unhindered through it and leaves the beam splitterand beam combination unit 1 through the exit surface 12 which isopposite the first entry surface 10 essentially in the same direction inwhich it entered it. Furthermore it is apparent from FIG. 1 that thelinear polarization of the component beam pencil 7 c, 7 d after passingthrough the polarization rotation element 3 is rotated by 90° and ispolarized in the Y direction according to the arrows 13 which point intothe plane of the drawings or project out of it. The component beampencil 7 c, 7 d which is likewise incident at an angle of 45° on theboundary surface 6 thus compared to the component beam pencil 7 a, 7 bhas a linear polarization direction which has been rotated by 90° sothat the component beam pencil 7 c, 7 d is totally reflected on theboundary surface 6. Therefore the component beam pencil 7 a, 7 b and 7c, 7 d in the area of the boundary surface 6 combine and emerge jointlyfrom the exit surface 12, as is shown schematically in FIG. 1. Itbecomes clear from FIG. 2b that the cross section 14 of the light beam 7emerging from the beam shaping unit has been reduced in size by one halfin the X direction, conversely the extension of the beam in the Ydirection was preserved. This is due to the fact that the component beampencils 7 a, 7 b and 7 c, 7 d after emerging from the beam shaping unitcompletely overlap; this among others also results in that the beam 7 isunpolarized after emerging from the beam shaping unit. In FIG. 2b thelinear polarization directions 9, 13 of the two component beam pencils 7a, 7 b which contribute to the cross section 14 are indicated. They arepolarized perpendicular to one another so that ultimately an unpolarizedlight beam 7 emerges from the beam shaping unit or the device.

[0036] It is quite possible in a device to arrange several of the beamshaping units shown in FIG. 1 in succession, the cross section of thelight beam passing through this beam shaping unit being shapedaccordingly, especially cut in half in one direction.

[0037]FIG. 3 shows another embodiment of a device as claimed in theinvention which comprises a beam shaping unit of somewhat differentstructure. This beam shaping unit in turn has a beam splitter and beamcombination unit 1 which corresponds to the beam splitter and beamcombination unit 1 from FIG. 1. Furthermore the beam shaping unit hasbeam deflection means which comprise a mirror 15 and a prism 16. Theprism 16 is arranged such that it is used additionally as a polarizationrotation element, as becomes clear from the following description.

[0038]FIGS. 3a and 3 b show a light beam 17 which is running from theleft in the Z direction onto the beam shaping units and which isillustrated by component beams 17 a, 17 b, 17 c and 17 d which have beenextracted by way of example. The beam splitter and beam combination unit1 and the mirror 15 are located offset to one another in the X and Ydirection so that the mirror 15 borders the edge of the beam splitterand beam combination unit 1 which extends in the Y direction, as isclearly apparent especially from the overhead view in FIG. 3a. In thisway the light beam 17 which is running in FIG. 3a from the left onto thebeam shaping unit with the component beam pencil 17 a, 17 b which is thetop one in FIG. 3a will run past the mirror 15 and will be incident onthe first entry surface 18 which is the X-Y surface in the illustratedcoordinate system. This component beam pencil 17 a, 17 b correspondingto the component beam pencil 7 a, 7 b in FIG. 1 passes essentiallyunhindered through the boundary surface 6 and the beam splitter and beamcombination unit 1 and leaves it through the opposing exit surface 19.

[0039] The component beam pencil 17 c, 17 d which is the lower one inFIG. 3a is incident in the Z direction in front of the beam splitter andbeam combination unit 1 on the mirror 15 which is located at an angle of45° to the Z direction and is deflected by it to the top in the Ydirection, as is apparent from FIG. 3b. Directly above the mirror 15 andthe beam splitter and beam combination unit 1 the prism 16 is located onthem. The prism 16 in the illustrated embodiment has two base surfaces20 which are made as isosceles right triangles and three rectangularprism surfaces 21, 22, 23. The prism 16 is thus arranged such that thecomponent beam pencil 17 c, 17 d which is reflected up by the mirror 15enters the prism 16 through the prism surface 21 which is formed by thehypotenuses of the base surfaces 20, this prism surface 21 in theillustrated coordinate system being an X, Z surface and resting at leastin sections on the top of the beam splitter and beam combination unit 1which is made as a polarization cube. Furthermore the prism 16 isaligned such that the hypotenuses of the base surfaces 20 with the sidesof the upper cube surface of the beam splitter and beam combination unit1 include an angle of 45°. Furthermore, the prism is aligned such thatthe projection of the apex line 24 of the prism into the XZ planeexactly intersects the connecting area between the beam splitter andbeam combination unit 1 and mirror 15, as is clearly apparent from theoverhead view as shown in FIG. 3a.

[0040]FIG. 3 furthermore indicates that the component beam pencil 16 c,16 d entering the prism 16 from underneath is reflected on the two prismsurfaces 22, 23. Optionally these prism surfaces can additionally bemirrored. From the second of these prism surfaces, i.e. from the surface23, the component beam pencil 17 c, 17 d is reflected downward andleaves the prism surface 21 which has been formed as the connectingsurface between the hypotenuses down in the negative Y direction andenters the beam splitter and beam combination unit 1 through its uppercube surface which is used as the second entry surface 25.

[0041] As a result of the above described arrangement of the prism 16the component beam pencil 17 c, 17 d in double reflection on the prismsurfaces 22, 23 is deflected not only from above into the beam splitterand beam combination unit 1, but also turned by 90° in itself. Thisrotation by 90° will be indicated by the two cross-hatched surfaces 26,27 which are shown in FIG. 3a. These cross-hatched areas 26, 27 roughlyreproduce the cross section of the component beam pencil which extendsbetween the beams 17 c and 17 d after reflection in the Y direction orthe −Y direction. As is apparent from FIG. 3a, the two cross-hatchedareas 26, 27 are turned by an angle of 90° to one another.

[0042]FIG. 3b likewise shows the direction of the linear polarization ofthe light beams 17 in the Y-direction by means of arrows 28. As islikewise indicated on the right side in FIG. 3b, the component beampencil 17 c, 17 d also undergoes rotation of the polarization directionby the 90° rotation in the prism 16 so that the component beam pencil 17c, 17 d after passing through the prism 16 in the X direction islinearly polarized, as is indicated by the arrows 29. As a result of thelinear polarization of the component beam pencil 17 c, 17 d which isperpendicular to the polarization of the component beam pencil 17 a, 17b it is reflected on the boundary surface 6 and leaves the beam splitterand beam combination unit 1 from the same exit surface 19 from which thecomponent beam pencil 17 a, 17 b emerges.

[0043]FIG. 4a shows the cross section 30 of the light beam 17 enteringthe beam shaping unit. After passing through the beam shaping unit thelight beam 17 has the cross section which is shown in FIG. 4b and whichrepresents overlapping of the cross section 31 of the component beampencil 17 a, 17 b which extends essentially in the X direction and ofthe cross section of the component beam pencil 17 c, 17 d which extendsessentially in the Y direction. Therefore the cross section 31 isessentially cross-shaped. The arrows 28, 29 indicate that the light beam17 leaving the beam shaping unit is likewise unpolarized at least insections. FIG. 4b moreover clearly shows that the component beam pencil17 c, 17 d has been turned with respect to its cross section by 90° asit passes through the prism 16.

[0044] It is also quite possible to place several of the beam shapingunits shown in FIG. 3 in succession so that the light beams passingthrough this device experience a corresponding change in cross sectionin each of the beam shaping units. Furthermore, it is also possible in adevice as claimed in the invention to place the beam shaping units ofthe type shown in FIG. 1 with beam shaping units of the type shown inFIG. 3 in succession.

[0045] Furthermore, there is the possibility of using units with similaraction as the beam splitter and beam combination unit 1 instead of thepolarization cube shown in FIG. 1 and FIG. 3. For example, aGlan-Thompson prism could be used. What is important is the fact thatthis beam splitter and beam combination unit consists of two parts,between which there is a boundary surface. Furthermore the boundarysurface must reflect in a linear polarization-selective manner at agiven angle the light beams incident on it by means of a certainwavelength or allow them to pass essentially unhindered. In order toachieve this action, as already described, double-refracting materialsare suited which with respect to their optical axis or their opticalaxes are aligned such that polarized beams on a boundary surface formedfor example by putty are reflected or passed essentially unhinderedaccording to their polarization.

[0046] Furthermore, as claimed in the invention it is possible toarrange several beam shaping units next to one another. In this way thelight beams emerging from the light sources located next to one anothercan be shaped at the same time upon passage through the beam shapingunits which are next to one another. One example of these light sourceswhich are next to one another is a laser diode bar which generally hasline-shaped emission sources of laser light which are located at equaldistances next to one another.

[0047] Especially in the beam shaping unit shown in FIG. 3 is itpossible to form an array 32 of prisms 16, as is shown in FIG. 5. InFIG. 5 the cross-hatched surfaces 26, 27 which are shown in FIG. 3a areindicated. It is thus possible by means of the array 32 for example inan analogous structure to FIG. 3a to implement with a beam splitter andbeam combination unit 1 made as a polarization cube and a mirror 15 ahost of beam shaping units which are located next to one another andwhich can shape the light beams proceeding from the light sourceslocated next to one another according to FIG. 3 to FIG. 4.

[0048] It is furthermore possible to use a prism 16 as a beam rotationunit, which can be used separately for light beams, this beam rotationunit being able to rotate a light beam by 90°. Compared to beam rotationunits, which are known from the prior art the use of a prism 16represents an exceptionally economical alternative.

[0049] In particular an array 32 of prisms 16 can be used as the beamrotation unit for the light beams which are located next to one anotherand which proceed from a laser diode bar. The light beams emerging fromthe array 32 of prisms 16 are offset in parallel relative to theoriginal light beams and move out of the array 32 opposite the entrydirection. This is clearly apparent in FIG. 5 in which for example thecross-hatched surfaces 26 can reproduce the cross section of the lightbeams which are moving out of the plane of the drawings in onedirection, conversely the crosshatched areas 27 which correspond to thebeams emerging from the array 32 reproduce the cross section of thebeams which are moving into the plane of the drawing. It is apparentthat in addition to the rotation of the cross section, offsetting of thelight beams to the right and top in FIG. 5 has taken place. With thecorresponding arrangement for example of a laser diode bar in front ofthe entry surfaces of the array 32 accordingly the light beams emergingfrom the array 32 could be guided for example away via the laser diodebar.

What is claimed is:
 1. A device for shaping the cross section of a lightbeam, comprising at least one beam shaping unit with beam splittermeans, beam deflection means and beam combining means, the beam splittermeans being able to divide the light beam which is incident on the beamshaping unit into two component beams, the beam deflection means beingable to deflect at least one of the component beams onto the beamcombining means, and the beam combining means being able to combine thetwo component beams, such that the cross section of the light beamemerging from the beam shaping unit compared to the light beam enteringthe beam shaping unit is reduced in at least one direction (X), whereinthe beam combining means is made as a polarization-selective beamsplitter and beam combination unit which comprises at least two partswith a boundary surface which is located between them, and the twoseparated component beams are incident on the boundary surface fromdifferent directions, and depending on their linear polarization one ofthe component beams pass the boundary surface unhindered and the otherof the component beams are reflected on the boundary surface so that thetwo component beams are combined in the area of the boundary surface andleave the beam splitter and beam combination unit essentially at thesame location in the same direction.
 2. A device as claimed in claim 1,wherein the beam splitter and beam combination unit consists at least insections of a double-refracting material.
 3. A device as claimed inclaim 1, wherein the beam splitter and beam combination unit is made asa Glan-Thompson prism.
 4. A device as claimed in claim 1, wherein thebeam splitter and beam combination unit is made as a polarization cube,the polarization cube consisting of two essentially identical prism-likeparts which form a boundary surface along one diagonal surface of thecube with one another.
 5. A device as claimed in claim 1, wherein atleast one of the two prism-like parts is provided with apolarization-selective coating in the area of the boundary surface.
 6. Adevice as claimed in claim 1, wherein the beam shaping unit comprises apolarization rotation element which can rotate the linear polarizationof one of the two component beams, especially by an angle of 90°.
 7. Adevice as claimed in claim 6, wherein the polarization rotation elementis made as a half wavelength plate.
 8. A device as claimed in claim 6,wherein the polarization rotation element is made as a prism which isarranged such that the cross section of the corresponding component beamis turned during passage through the prism, especially by 90°, in thisway the corresponding rotation of the linear polarization of thiscomponent beam taking place.
 9. A device as claim 1, wherein the beamsplitter and beam combination unit is located in the beam path of thelight beam which is incident on it such that it is used both as a beamsplitter means and also a beam combination means in which the firstcomponent beam is incident directly on the first entry surface of thebeam splitter and beam combination unit, conversely the second componentbeam can run past the first entry surface and can be deflected by thebeam deflection means onto the second entry surface.
 10. A device asclaimed claim 1, wherein the beam deflection means comprises a mirrorwhich is located preferably at an angle of 45° in the second of the twocomponent beams.
 11. A device as claimed in claim 1, wherein the beamdeflection means comprises a prism in which the corresponding componentbeam is reflected, especially reflected twice.
 12. A device as claimedin claim 11, wherein prism is used at the same time as a polarizationrotation element and as a deflection means.
 13. A device as claimed inclaim 12, wherein the prism, the mirror and the beam splitter and beamcombination unit are arranged such that a component beam can be directlyincident on the first entry surface of the beam splitter and beamcombination unit, conversely the second component beam is reflected bythe mirror into the prism, in which the beam cross section of thecomponent beam is turned by 90° and from which the component beam canenter the second entry surface of the beam splitter and beam combinationunit.
 14. A device as claimed in claim 1, wherein the device comprisesmore than one beam shaping unit which are located in succession suchthat the cross section of the light beam changes in each of the beamshaping units, especially can be reduced in one direction.
 15. A deviceas claimed in claim 1, wherein the device comprises more than one beamshaping unit which are located next to one another such that light beamsemerging from the light sources which are next to one another can bechanged in the beam shaping units located next to one another, inparticular can be made smaller in one direction.
 16. A device as claimedin claim 15, wherein the beam shaping units located next to one anothercomprise an array of prisms, each of the individual prisms of the arraybeing used at the same time as a polarization rotation element and as adeflection means of each of the individual beam shaping units.
 17. Anarrangement for coupling a light beam which proceeds from an elongatedlaser light source with an elongated cross section into an opticalfiber, comprising a laser light source, at least one collimation unitfor collimating the light beam which emerges from the laser lightsource, and at least one focusing unit for focusing the light beams ontoan optical fiber, wherein the arrangement furthermore comprises a devicewhich is located in the beam path of the light beam as claimed inclaim
 1. 18. A beam rotation unit for a device as claimed in claim 1,the beam rotation unit comprising at least one prism which can belocated in the beam path of at least one light beam such that the crosssection of the light beam passing through at least one prism can beturned by at least two reflections, especially rotation by 90° beingable to take place, wherein at least one prism has two base surfaceswhich are made as isosceles right triangles and three rectangular prismsurfaces, and the light beam passing through at least one prism can bereflected on the two prism surfaces which extend between the legs of thebase surfaces.
 19. A beam rotation unit as claimed in claim 18, whereinthe beam rotation unit comprises a number of prisms which are combinedinto an array so that the cross sections of the light beams proceedingfrom the light sources which are located next to one another can berotated.